Safety controls for fuel burners



Aug. 29, 1967 K 3,338,287

SAFETY CONTROLS FOR FUEL BURNERS Filed Feb. 24, 1966 GAS FIG-2 IIOVAC. 52

55 RESONANT CIRCUIT INVENTOR. LORIS D. CLARK ATTORNEYS United States Patent Ofiice 3"338,287 Patented Aug. 29, 1967 3,338,287 SAFETY CONTROLS FOR FUEL BURNERS Loris D. Clark, Dayton, Ohio, assignor to Master Consolidated Inc., Dayton, Ohio, a corporation of Ohio Filed Feb. 24, 1966, Ser. No. 529,722 6 Claims. (Cl. 158-28) ABSTRACT OF THE DISCLOSURE This invention relates to safety controls for fuel burners and more particularly to an improved control for monitoring the operation of fuel burners, such as gas burners and the like.

In many installations, particularly in low cost, lightweight portable fuel burning units, it is important that dependable safety controls be provided to shut down the operation of the unit, and particularly the supply of fuel, in the event that the flame does not ignite automatically or, for some reason, extinguishes during the operation of the unit. While manually operable controls are commonly employed with continuous pilot lights and the like in which an override is manually depressed until the flame is lit and well established, these controls and overrides are not suited for fully automatic operation in oil or gas fired heaters which start and stop automatically or in response to plugging into a power line, and in which there can be no continuous pilot light.

This invention provides a safety control system and circuit in which provision is made for the ignition of fuel at a burner, but if the fuel fails to ignite following a short period of time, or if the flame becomes extinguished after ignition, the fuel valve is promptly closed. The invention particularly employs a circuit breaker through which an electric fuel valve is operated and which is caused to substantially overload upon the failure of the fuel to ignite or upon subsequent extinction of the flame, so that the circuit breaker is tripped to interrupt a circuit to the fuel valve. Further, the system employs a series resonant circuit by the inclusion of a capacitor in series with the operating coil of the fuel valve, thereby effectively eliminating from the circuit the impedance caused by the inductance of the valve, providing a circuit which is operable in response to the resistance in the circuit, apart from the inductance of the fuel valve. In this manner, the circuit breaker can be caused to operate at or near its rated capacity during normal operation of the burner for pre-heating the circuit breaker so that it responds rapidly to a substantial increase in load as a result of the closing of the flame detector contacts.

It is accordingly an object of this invention to provide a safety control circuit for a fuel burning space heater in which the fuel valve coil forms a part of a series resonance circuit.

A more specific object of this invention is the provision of a safety control in which a capacitor is placed in series with the operating coil of a fuel valve forming a series resonance circuit at line voltage frequency substantially reducing the affects of coil inductance.

A further object of this invention is the provision of a foolproof, fail safe, and low cost safety control for fuel burners which is particularly adapted for use in portable gas fired space heaters.

A still further object of this invention is the provision, in a safety control as outlined above, of a further switch responsive to the flow of air from a blower connected to open the electric circuit to the fuel valve upon the decrease or failure of such air flow.

A more specific object of the invention is the provision of a safety control circuit in which the heater of a circuit breaker is operated in series with the holding coil of a fuel valve, and in which a flame detector circuit operates substantially to increase the load on the circuit breaker heater in excess of the rated capacity of the circuit breaker upon failure or extinction of the flame, but which prevents the opening of the fuel valve upon the failure of the flame detector.

These and other objects and advantages of the present invention will be apparent from the following description,

. the accompanying drawings, and the appended claims.

In the drawings:

FIG. 1 is a vertical section through a portable gas-fired space heater having a safety control system according to this invention; and

FIG. 2 is an electrical wiring diagram of the safety control circuit.

Referring to the figures of the drawing which illustrate a preferred embodiment of the invention a portable space heater is illustrated generally at 10 in FIG. 1 as including an outer air shroud 11 within which is contained a stainless steel combustion chamber -12. A gas burner housing 14 is mounted on a rear Wall of the combustion chamber 12 and includes a suitable nozzle, not shown, adapted to admit low pressure gas for burning within the chamber 12. An annular air space 15 is provided around the combustion chamber 12 by means of which heat is extracted from the chamber and expelled through the front 16 of the shroud 11.

The space heater 10 further includes a fan motor 18 and a shrouded fan 19 which supplies both the air for general circulation over the chamber 12, and the combustion air into the interior of the combustion chamber for mixing and burning with the fuel. For this purpose, there are provided suitable openings (not shown) in the burner housing 14 for admitting air from the fan 19 into the interior of the combustion chamber 12 for mixing with the gas and providing an excess of combustion air.

Ignition is accomplished by a pair of electrodes 20 in burner housing 14 which are electrically connected to the secondary of an ignition transformer 21. Gas or fuel from a suitable source of low pressure gas is admitted at line 25 to a solenoid coil-operated gas valve 26. From this valve the gas flows through a pipe 27 to the burner 14.

The space heater 10 may conveniently be provided with a front handle 30 which forms depending'front legs 31 for supporting the front of the heater. The rear of the heater may be conveniently mounted for portability on wheels 32. A pan-like housing 35 extends beneath the heater shroud 11 and contains the gas valve 26, the transformer 21 and certain of the remaining controls associated with this invention.

A flame detector 36 is shown as being mounted on the combustion chamber 14 and includes a sensor 37 extending into the interior of the chamber. The flame detector 36 includes electric contacts which are normally closed, but are opened by suflicient heating at the probe 37 to indicate the presence of a flame within the combustion chamber 12.

Means for monitoring the operation of the motor 18 and the fan 19 includes a normally open switch 40 which has a flag or sail 41 connected on the switch arm and positioned upstream of the fan 19 but within the shroud in FIG. 2 as including a thermally-operated resettable circuit breaker 50 which has its normally closed contacts 51 connected in the electrical supply line 52 leading to the heater 10, and which has its current-sensitive element or heater 53 connected in series with the gas valve coil 26. The sail switch 40 and the flame detector switch 36 are also shown as being connected in series with the heater 53 and the holding coil of the gas valve 26. The contacts of the flame detector switch 36 are bypassed by a parallel-connected resistor 55.

Means forming a series resonant circuit with the valve 26 includes a capacitor 60 which is connected directly in series therewith. The coil of the valve 26 and the capacitor-60 form a series-resonant circuit at the line frequency, and the components are therefore chosen to resonate at such line frequency. For example, it has been found that on'a 60 cycle line, a gas valve having an inductance of two henrys may be used with a capacitor 60 having a capacitance of two microfarads. The series-resonant circuit which is formed thereby is placed effectively in series with the heater 53 of the circuit breaker 50 and with the flame detector circuit comprising the switch 36 and resistor 55.

Preferably, the ignition transformer 21 and the fan motor 18 are connected in parallel across the line 52. Each is controlled by the contacts 51 of the circuit breaker 50.

In the operation of the circuit shown in FIG. 2, when power is applied to the line 52, the transformer 21 and the motor 18 are immediately energized through the normally closed contacts of the circuit breaker 50. Also, power is applied to operate the gas valve 26 through the heater 53 of the circuit breaker 50, the closed sail switch contacts 40 and flame detect-or contacts 36. This heating load on the circuit breaker 50 is substantially in excess of its rated capacity, and may be, for example, 270% in excess of the circuit breaker rating. However, since the circuit breaker is cold (has not been pro-heated) it will readily withstand this overload without opening for a sufficient time, such as 10 and 15 seconds, to permit normal firing of the burner 14, followed by opening of the flame detector contact 36. If for any reason the burner fails to ignite, the circuit breaker 50 will be tripped, thereby shutting off the power to the heater and closing the gas valve 26.

However, if the flame should ignite normally, the flame detector switch is opened placing the resistor 55 in the circuit. This resistance, together with that of the heater 53, is such as to permit sufficient current to flow through the series-resonant circuit to maintain the gas valve 26 in its operated condition. However, the current flowing through the entire holding circuit is substantially independent of the impedence due to the inductance of the gas valve holding coil, due to the series resonant circuit in which it is associated. The resistance 55 can therefore be chosen so that the circuit breaker is operated at or near its rated load, such as 91 to 96% of its rated capacity. In this condition, the circuit breaker is effectively preheated. Accordingly, extinction of the flame at the burner, resulting in the closing of the flame detector switch 30, immediately places a substantial overload on the circuit breaker causing the same to open within a comparatively short time of 3 to 5 seconds. Since the sail switch 40 is also in series with the gas valve 26, failure of either the motor 18 to start or failure of air delivery causes immediate opening of this switch and closing of the gas valve 26.

The circuit shown in FIG. 2 is one which is fail-safe. If the contacts of the flame detector 36 should stick in the closed position, and the operation of the heater started, the overload on the circuit breaker 50 would cause the system automatically to shut down. On the other hand, while the current through the resistor 55 is suflicient to hold the valve 26 open once it has been opened by current through the contacts 36, the current through the resistor 55 alone is not suificient to open the valve. This is due to the fact that it normally takes considerably less current to hold a solenoid-operated gas valve in its open or operated position than it takes to open the valve initially. Accordingly, if the flame detector contacts 36 should stick in the open position, the heater cannot be ignited.

For example, satisfactory operation has been achieved with a resistor 55 of 1500 ohms, in which the resistance of the circuit breaker heater 53 was approximately 250 ohms and in which the rated current through the heater was 50 milliamps. A current of from below 40 to above 50 milliamps was found sufficient to hold the gas valve in the operated position but was not suificient to operate the gas valve initially, with the flame detector contacts 36 open. Further, it has been found that the controls operate dependably over wide fluctuations in line voltage, and voltages as low as volts provide normal ignition and operation while a line voltage as high as volts will not operate the valves 26 with the flame detector switch 36 stuck in the open position.

It will therefore be seen that this invention provides a low-cost fool-proof safety control which is adaptable for use with portable space heaters, and which may also be used on other types of automatic fuel fired equipment, to provide rapid shut-down in the event of malfunction. The employment of the capacitor 60 provides a control circuit in which there is greater control over the current flow through the heater 53 due to the substantial elimination of the IX drop across the coil 26, resulting in a wider difference in current between conditions in which the switch is open and closed. This permits a rapid and substantial overload to be applied in one condition and operation at or near rated value in the others.

While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. A safety control for controlling the operation of a fuel burner from an AC source of power and for quickly stopping the flow of fuel to the burner upon the failure of the burner to ignite or upon extinction of the flame subsequent to ignition, comprising a fuel valve having an electrically operated holding coil, a circuit breaker having its contacts connected in controlling relation to the fuel valve and having a heater element connected in series with such valve holding coil, capacitor means connected effectively in series with said holding coil and forming a series resonant circuit with said coil of relatively'low impedance at the frequencies of said source, a flame detector switch circuit including a pair of normally closed contacts and a resistor connected in parallel with said contacts, said circuit being connected in series with said fuel valve, said capacitor means, and said heater and operable in a first position in the absence of a flame at the burner to place a relatively high l ad on said heater in excess of the rated current capacity of said circuit breaker, and further operable upon the presence ofa flame at said burner to open said contacts to apply a substantially decreased load through said resistor on said heater so that failure of the burner. to ignite or extinction of the flame subsequent to ignition causes an increased current load to be applied to said circuit breaker in excess of its rating providing quick opening of said circuit breaker, said increased current load being substantiall independent of the reactance of said holding coil.

2. A safety control for controlling operation of a fuel burner and for quickly stopping the flow of fuel to the burner upon the failure of the burner to ignite or upon extinction of the flame subsequent to ignition, comprising a fuel valve having an electrically operated holding coil,

a circuit breaker connected in controlling relation to the fuel valve and having a current-responsive element connected in series with such valve holding coil, a capacitor connected in series with said holding coil forming a series-resonant circuit therewith substantially at the frequency of the line voltage so that the current flowing through the current responsive element of the circuit breaker is substantially independent of the inductance of the holding coil, a flame detector circuit connected in series with said fuel valve and said current responsive element and operable in a first state in the absence of a flame at the burner to place a relatively high load on said current sensing element in excess of the rated current capacity of said circuit breaker, and further operable upon the presence of a flame at said burner to apply a substantially decreased load on said current sensing ele ment so that failure of the burner to ignite or extinction of the flame subsequent to ignition causes an increased current load to be applied to said circuit breaker in excess of its rating providing quick opening of said circuit breaker.

3. The control of claim 2 in which said flame detector circuit includes a flame detector switch having normally closed contacts connected in series with said fuel valve which open in the presence of a flame in the burner, and

resistance means connected in parallel with said flame detector contacts providing for the continued operation of said fuel valve by current flowing therethrough subsequent to the opening of said normally closed flame detector contacts.

4. The safety control of claim 1 further including a blower for supplying air to the burner, and a sail switch positioned in the inlet air stream of said blower and having normally open contacts connected in series with said fuel valve coil which close with the proper operation of said blower to apply power to said coil.

5. The safety control of claim 2 further including a blower for supplying air to the burner, and a sail switch positioned in the air stream of said blower and having normally open contacts connected in series with said fuel valve coil which close with the proper operation of said blower to apply power to said coil.

6. The control of claim 5 in which said said switch is positioned upstream of the flow of air into said blower.

References Cited UNITED STATES PATENTS 2,195,650 4/1940 Hardy 15828 2,412,990 12/ 1946 Kruse.

3,051,161 8/1962 Hicks 15842.2 X 3,056,398 10/1962 Kirk 158422 X 3,079,984 3/1963 Wright et al 158l25 3,207,204 9/1965 Thompson 15828 X 3,270,800 9/1966 Deziel et a1. 158-128 JAMES W. WESTHAVER, Primary Examiner. 

1. A SAFETY CONTROL FOR CONTROLLING THE OPERATION OF A FUEL BURNER FROM AN AC SOURCE OF POWER AND FOR QUICKLY STOPPING THE FLOW OF FUEL TO THE BURNER UPON THE FAILURE OF THE BURNER TO IGNITE OR UPON EXTINCTION OF THE FLAME SUBSEQUENT TO IGNITION, COMPRISING A FUEL VALVE HAVING AN ELECTRICALLY OPERATED HOLDING COIL, A CIRCUIT BREAKER HAVING ITS CONTACTS CONNECTED IN CONTROLLING RELATION TO THE FUEL VALVE AND HAVING A HEATER ELEMENT CONNECTED IN SERIES WITH SUCH VALVE HOLDING COIL, CAPACITOR MEANS CONNECTED EFFECTIVELY IN SERIES WITH SAID HOLDING COIL AND FORMING A SERIES RESONANT CIRCUIT WITH SAID COIL OF RELATIVELY LOW IMPEDANCE AT THE FREQUENCIES OF SAID SOURCE, A FLAME DETECTOR SWITCH CIRCUIT INCLUDING A PAIR OF NORMALLY CLOSED CONTACTS AND A RESISTOR CONNECTED IN PARALLEL WITH SAID CONTACTS, SAID CIRCUIT BEING CONNECTED IN SERIES WITH SAID FUEL VALVE, SAID CAPACITOR MEANS, AND SAID HEATER AND OPERABLE IN A FIRST POSITION IN THE ABSENCE OF A FLAME AT THE BURNER TO PLACE A RELATIVELY HIGH LOAD ON SAID HEATER IN EXCESS OF THE RATED CURRENT CAPACITY OF SAID CIRCUIT BREAKER, AND FURTHER OPERABLE UPON THE PRESENCE OF A FLAME AT SAID BURNER TO OPEN SAID CONTACTS TO APPLY A SUBSTANTIALLY DECREASED LOAD THROUGH SAID RESISTOR ON SAID HEATED SO THAT FAILURE OF THE BURNER TO IGNITE OR EXTINCTION TO THE FLAME SUBSEQUENT TO IGNITION CAUSES AN INCREASED CURRENT LOAD TO THE APPLIED TO SAID CIRCUIT BREAKER IN EXCESS OF ITS RATING PROVIDING QUICK OPENING OF SAID CIRCUIT BREAKER, SAID INCREASED CURRENT LOAD BEING SUBSTANTIALLY INDEPENDENT OF THE REACTANCE OF SAID HOLDING COIL. 